Cloud computing is a fast-emerging area with so many benefits for the end users. Many leading firms make use of cloud mainly to store their huge volume of data and other such purposes. When speaking about cloud, we need to focus on the data centers. This is because the virtual machines (VM) present in the cloud are mapped to the physical devices that are present in the data centers. This seems to be a simple process, but the tricky part is when the number of users increases. Number of users send the request for a particular or more than one service to the cloud. The service providers have to handle the entire request and also concentrate on the satisfaction of the end user along with the quality of service (QoS). Most important thing is that the service provider must give a quick response to the cloud consumers, i.e., the delay must be minimized. Only then the QoS provided could be maintained. In this paper, we are going to see about how the tasks are being scheduled and allocated optimally to the VMs present in the cloud. We are going to delineate the various algorithms that are implemented so far for this process. In this paper, we have described an overview of cloud, task scheduling and VM allocation.